This invention relates to an internal combustion engine and, more particularly, to an internal combustion engine having a cylinder section which may be pivoted with respect to the crank case section thereof to vary the compression ratio of the engine.
In engine technology it is known, of prior art, that an engine with a variable compression ratio can improve the efficiency of the engine, particularly when the engine is operated on partial load, enabling the maximum performance of the engine to be increased considerably.
There are a number of different basic solutions for providing adjustment of the compression ratio of an engine. The American patent specification U.S. Pat. No. 2,770,224 describes a piston engine with a fixed crankcase section, to which is hinged a cylinder section, with associated cylinder head. Under is the influence of an eccentric shaft the cylinder section can be pivoted to a greater or lesser degree about a longitudinal shaft, enabling the volume of the combustion chamber to be varied.
In the engine shown the cylinder section is hinged to the crankcase section by means of a hinge shaft which may also be regarded as constituting a central shaft for the engine camshaft. This is advantageous because the mechanism for controlling the engine valves by means of the camshaft, and in this case also push rods, is not therefore appreciably affected by the fact that the cylinder section is hinged.
Although an engine of this design may be regarded as favourable from the point of view of combustion, it nevertheless suffers from several disadvantages which limit its potential for practical application.
The possibilities of arranging a perfect seal between the cylinder section and the crankcase section are limited. Because the divisions between the two sections extend in different planes around the periphery of the engine, it is necessary to arrange seals which also extend in the vertical direction of the engine. On one side of the engine the seals will be subjected to torsional forces, whilst the seals on the other side are subjected to combined tens le and bending stresses. There is no suitable material for simultaneously meeting these requirements, but it is probably necessary to arrange such types of seals at different points along the divisions. This in turn creates problems in connecting the seals to each other. A good seal between the cylinder section and the crankcase section is essential both for preventing the ingress of dirt in the crankcase and for preventing oil and/or gases present in the crankcase from leaking out.
Internal combustion engines for vehicle use are also used to drive a number of different auxiliary units, e.g. generator, servo pumps, compressor and water pump. In engines with a fixed compression ratio these components are secured to the cylinder section of the engine by means of various brackets, and are driven by the crankshaft of the engine by means of belt transmissions. In an engine with a moving cylinder section this is not possible unless complicated arrangements are provided for their drive. The above-mentioned patent specification U.S. Pat. No. 2,770,224 does not provide a solution for arranging this in practice either.
In an engine for vehicle use the output shaft of the engine is connected by a clutch to a gearbox. The possibilities in practice of arranging a flange plane for securing a clutch case or gearbox to one end of the engine are similarly limited if the cylinder section of the engine is moving. Internal combustion engines for use other than in vehicles present similar problems.